From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 765CA284B25 for ; Thu, 20 Nov 2025 10:39:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763635170; cv=none; b=sP/aYjM3StBY7/aLLu7Zh2uPOuBf/qAPkaCPgN7YisSPPmM8OCBEnUGNfodynAk3CLwEH0ummHusx4CXF+DMJX30LALnT8Q5XYBhk0RVnXK6CPcToBge4xTtDmcH5GF8uzw/LgYekRZyr2X1FzhXJ9aUxMe2yOwAud0vX3bc/Do= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763635170; c=relaxed/simple; bh=znEBJZ6KVjGxzXOPPFRsG2pfUqSyfqKNp3vpnt4GJOI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=IDBViFaofkp3Eax4gNget9cl4ZpK+RhXjznlml1P40j/KqiOyz41mGlRb5exHnD1BvzS6MbrwmKxXKF4QMOLNm8vHARJcUBEKM60r05jwvSMDRCZO5oWjQ4NX4nFl2sJ69X/T5lpoL0IXYX+ApMYetzCiP5iSdJYrDlOMnolkxM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=d+NMVcBn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="d+NMVcBn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E52C5C4CEF1; Thu, 20 Nov 2025 10:39:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763635169; bh=znEBJZ6KVjGxzXOPPFRsG2pfUqSyfqKNp3vpnt4GJOI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=d+NMVcBnQBzC7bjU9SGmlKCg9QD1FjOqHhljO7/dgmuvdk6VrTEKwWCW4phwfHHd8 PB3TCRF0Zex+ImdB5soewloNhAA6U9XfQmF+FVBbt0wyqpGM3lMM6z48PXFeXL5gDu oJHDekD5xXDH236W2gsv2C379JPZuS3UyL9zMlS2KjQF5bPKguchJ3gVDC43qr1cLM zIoixbl2+j+a3DuJYs9R6KwP9+Vu2T/aHyyqC7tnGm+Bo/2VnFXgvtKzcowKux1Urs B9lLldl/SE9NXZ6sEEqCAuT+5Cm6KFGrg8iX0WFXCJV3QfpwtPoD0hHRKo0f7BTyO3 A5dE/feCtJxBQ== Date: Thu, 20 Nov 2025 12:39:21 +0200 From: Mike Rapoport To: Pratyush Yadav Cc: Pasha Tatashin , akpm@linux-foundation.org, bhe@redhat.com, jasonmiu@google.com, arnd@arndb.de, coxu@redhat.com, dave@vasilevsky.ca, ebiggers@google.com, graf@amazon.com, kees@kernel.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v1 04/13] kho: Verify deserialization status and fix FDT alignment access Message-ID: References: <20251114155358.2884014-1-pasha.tatashin@soleen.com> <20251114155358.2884014-5-pasha.tatashin@soleen.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Tue, Nov 18, 2025 at 06:11:24PM +0100, Pratyush Yadav wrote: > On Tue, Nov 18 2025, Pasha Tatashin wrote: > > >> > This page is never freed, so adding it to zone managed pages or keeping it > >> > reserved does not change anything. > >> > >> In practice, sure. I still don't see a good reason to _not_ initialize > >> the page properly. It's not like it costs us much in terms of > >> performance or code complexity. > >> > >> Since kho_restore_folio() makes sure the folio was _actually_ preserved > >> from KHO, you have a safety check against previous kernel having a bug > >> and not preserving the FDT properly. And I get that the FDT has already > >> been used by this point, but at least you would have some known point to > >> catch this. > > > > The kho_alloc_preserve() API is different from kho_preserve_folio(). > > With kho_preserve_folio(), memory is allocated and some time later is > > preserved, so there is a possibility for that memory to exist and be > > used where it is not preserved, therefore it is a crucial step for > > such memory to also do kho_restore_folio() before used. With > > kho_alloc_preserve(), when the memory exists it is always preserved; > > it is gurantee of this API. There is no reason to do > > kho_restore_folio() on such memory at all. It can be released back to > > the system via kho_free_restore()/kho_free_unpreserve(). > > Even for those I think there should be a kho_restore_mem() or something > similar (naming things is hard :/), so they go through the restore, > their struct page is properly initialized and accounted for, and > make sure the pages were actually preserved. > > Using the memory without restoring it first should be the exception IMO. Base KHO and LUO FTDs are such exceptions for sure :) We have to use them way before we can even think about restoring. > -- > Regards, > Pratyush Yadav -- Sincerely yours, Mike.